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Robert,
I don't understand your suggestion.

> Is it possible Alex that the engraving for the zero mark
> is off by 9/10 of a minute?

You mean the fixed zero mark or the zero mark on the vernier?
The fixed zero mark error will have the same effect on all
measurements.
On the veriner, how can it be that zero mark is off
by 0.9 and all other marks on their place?
This would be easily visibe by naked eye.

>You get consistent errors at other
>measurements so this might be the only reasonable answer.

To investigate the matter further, I think I have to measure
small angles. The error is -0.3 at zero angle, it is about the same
at 30' angle (IC from Sun is consistent with IC from stars),
and suddenly it is almost -1' at approx 9 degrees (the smallest star
distance I measured). So something happens in between.

I tried to use the wires in my the scope which are about 2 degrees apart,
and the wire test gives the same error as the Index tests, that is
something -0.3 to -0.4. Unfortunately, the wires themselves are
about 0.2' thick:-)

I need some good stars at  2, 3..., 9 degrees apart which I hope
to identify using USNO Astro Almanac.

Alex.

   

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